This invention relates to a hollow structural beam that is filled with a heat sink. In particular, it relates to hollow rectangular steel beams filled with containers holding water.
The New York World Trade Center (WTC) towers destroyed in the terrorist attack of Sep. 11, 2001 were supported by exterior columns tied to a core of interior columns. Analysis of the collapse of the North and South Towers showed that the buildings withstood the initial impact of the two planes, despite the destruction of many exterior and interior columns. Insulation protecting the columns from heat, however, was blown off and the sprinkler system was destroyed. The jet fuel from the planes ignited, but it is believed that the jet fuel fire dissipated before weakening the columns. Paper, office furniture, carpets, and other combustibles continued to burn, however. When the temperature of the steel exceeded about 2000xc2x0 F., the columns buckled under the weight of the higher floors and the buildings collapsed.
Ideally, fire protection for steel beams should add little or no additional load to the beams. The fire protection should be in place all the time, so that there is no need to rely upon sprinkler systems for moving water to the fire, as such systems can easily be destroyed in an explosion. And the fire protection should be automatically replenished as it is consumed. These requirements seem impossible to meet, but meeting them is the object of this invention.
The fire resistant beams of this invention are tubes. The interior of the beams is filled with a material, such as water, that acts as a heat sink.
In a preferred embodiment, vertical beams according to this invention run the entire height of the building and the space inside the beams is continuous from the foundation all the way to the roof. Thus, the entire weight of the heat sink inside the beams rests on the foundation and none of the weight of the heat sink is carried by the beams. When a fire consumes the heat sink at any floor of the building, the entire remaining heat sink all the way to the roof slides down and replaces it.
For example, if the South Tower of the WTC had been protected by vertical beams according to this invention that had an interior space of one square foot, where the beams were filled with water, the fire on the 80th floor of the 110 story building would have had to vaporize at least 360 cubic feet of water (12 feet per floor, 30 higher floors) in each column before the temperature of the steel could even begin to rise above about 212xc2x0 F. At least 5.5 million Calories would be required to raise the temperature of that amount of water (10 m3) from 20xc2x0 C. (68xc2x0 F.) to 100xc2x0 C. (212xc2x0 F.), then vaporize it, and there was sufficient fuel to generate only a small fraction of that amount of energy.